(1) Field of the Invention
The present invention relates to composite insulators.
(2) Related Art Statement
A composite insulator having a structure as shown in FIG. 3 is known. That is, an elastic insulating material 12 is molded in the form of a rubber housing around the outer periphery of an insulating rod 10 made of a glass fiber-reinforced plastic (FRP) or the like. This housing includes a plurality of shed portions 11 (in FIG. 3, only one shed portion is illustrated). A pair of end fittings are fixedly crimped around respective end portions of the insulating rod 10 to partially hold these end portions. A straight portion 14 exists between an end of the end fitting 13 and an opposed shed portion 11 Straight portion 14 will be referred to hereinafter as "a sheath portion".
However, since the electric field concentrates near the end fitting 13, the sheath portion 14 of the elastic insulating material 12 tends to erode. This sheath portion 14 is thinner as compared with the shed portion 11, such that the insulating rod 10 is likely to be exposed through the erosion of this sheath portion 14. As a consequence, the insulating rod 10 deteriorates as a result of the exposure thereof.
In order to solve the above problem, a composite insulator having a structure as shown in FIG. 4 has been proposed. According to this composite insulator, an end fitting 15 is preliminarily crimped and fixed around each of opposite end portions of an insulating rod 16, and an elastic insulating material 17 is molded in the form of a rubber housing around the insulating rod 16 including parts of the end fittings 15. This composite insulator is constructed such that a shed portion 18 is continued to the end fitting 15 without a sheath portion 14 being interposed therebetween. Since the thickness of the shed portion 18 is thicker than the above-mentioned sheath portion, more tolerance is assured against the exposure of the insulating rod 16 even if the shed portion 18 suffers erosion.
However, in the latter conventional technique (FIG. 4), after the end fittings 15 are crimped around the insulating rod 16, the elastic rubbery insulating material 17 is molded. Therefore, since the insulating rod 16 experiences a certain heat history due to the heating during the molding process, fitting strength between the insulating rod 16 and the end fitting 15 decreases.